Energy reducing levels

We have seen that in a steady field Hq a small excess, no, of nuclei are in the lower energy level. The absorption of rf energy reduces this excess by causing transitions to the upper spin state. This does not result in total depletion of the lower level, however, because this effect is opposed by spin-lattice relaxation. A steady state is reached in which a new steady value, n, of excess nuclei in the lower state is achieved. Evidently n can have a maximum value of o and a minimum value of zero. If n is zero, absorption of rf energy will cease, whereas if n = no, a steady-state absorption is observed. It is obviously desirable that the absorption be time independent or. in other words, that s/no be close to unity. Theory gives an expression for this ratio, which is called Zq, the saturation factor ... 

It has been demonstrated that it is possible to lower the level of airborne radon progeny by filtering and/or expose the air to an electric field. If the radiological risk is measured by the potential alpha energy concentration (PAEC) or exposure rate, for instance expressed in J m 3 or WL, the level may be lowered to about 10-20 % of the value in untreated air, while the reduced level may only be about 40-50 % of the untreated one if the average dose to a certain part of the respiratory tract, for instance expressed in Gy year 1, is considered. 

At low and medium doses, it is well established that the nutritional value of proteins, carbohydrates, and fats as macronutrients are not significantly impaired by irradiation, and neither the mineral bioavailability is impacted. Like all other energy depositing process, the application of ionizing radiation treatment can reduce the levels of certain sensitive vitamins. Nutrient loss can be minimized by irradiating food in a cold or frozen state and under reduced levels of oxygen. Thiamin and ascorbic acid are the most radiation sensitive, water-soluble vitamins, whereas the most sensitive, fat-soluble vitamin is vitamin E. In chilled pork cuts at the 3 kGy maximum at 0-10°C, one may expect about 35 0% loss of thiamin in frozen, uncooked pork meat irradiated at a 7 kGy maximum at —20°C approx., 35 % loss of it can be expected [122]. 

Fig. 8.1 Glucose metabolism in coupled neuron and astrocyte system. ATP is produced via oxidative energy metabolism (glycolysis, TCA cycle and oxidative phosphorylation) in neurons and in astrocytes. Na+ entry during electrical activity initiates increased oxidative energy metabolism within neurons. The activation of neuronal Na+-K+ ATPase in the plasma membrane leads to reduced levels of ATP, which rapidly activates glycolysis. This process requires an elevated glucose level, which is transported via the neuronal glucose transporter (GT). The generated ATP can restore the Na+/K+ balance via Na+-K+ ATPase. The rapid increase of glycolysis results in increased NADH/NAD+ and increased cytoplasmic pyruvate. In astrocytes,...

Besides the variable functional outcome after ischemia in animal models, it is well established that specific neuronal populations within an individual vary substantially in ischemic tolerance. Neurons in the CA1 region of the hippocampus and other distinct cellular populations of the caudate, thalamus, neocortex and cerebellum are selectively vulnerable to relatively brief periods of ischemia (Kirino and Sano 1984 Siesjo 1988). The reasons for this phenomenon are not fully elucidated, but for example in cerebellar Purkinje cells it could be shown that a reduced level of aldolase may trigger energy failure after brief periods of anoxia (Welsh et al. 2002). Changes in microcirculation, as seen in focal stroke,... 

Tissues with particularly high oxygen and energy requirements, including the brain and heart, are particularly susceptible to harmful effects resulting from reduced levels of oxygen in the body. 

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